Flame retarding celluloscis using tetrakis (hydroxymethyl) phosphonium chloride

ABSTRACT

A process for imparting flame-retardant character to cellulosic containing material has been devised in which the cullolosic material is impregnated with an aqueous solution of a tetrakis(hydroxymethyl)phosphonium compound, preferably partially neutralized tetrakis(hydroxymethyl)phosphonium chloride, the impregnated material is at least partially dried, e.g., to about 5 to 25 percent by weight moisture retention, without fixation of the phosphonium compound on the material, the partially dried material is cooled and then treated with dry ammonia gas optionally in the presence of water vapor whereby the phosphonium compound is cured on the material and a fire-retardant character is imparted thereto.

United States Patent [191 Eggenweileret a].

TETRAKIS (HYDROXYMETHYL) PHOSPHONIUM CHLORIDE Inventors: Robert B.Eggenweiler, West Seneca; James J. Duffy, Buffalo, both of NY.

Hooker Chemical Corporation, Niagara Falls, NY.

Filed: Nov. 4, 1971 Appl. No.: 195,843

Assignee:

References Cited UNITED STATES PATENTS 9/1971 Beninate et al ll7/62.26/1957 Reeves et al 1 17/136 UX 8/1963 Ullman 1 17/622 Nov. 27, 19733,236,676 2/1966 Coates et al. ll7/62.2 3,421,923 l/l969 Guth ll7/136XPrimary Examiner-William D. Martin Assistant Examiner-J-larry J.Gwinnell AttorneyPeter F. Casella et al.

[57] ABSTRACT A process for imparting flame-retardant character tocellulosic containing material has been devised in which the cullolosicmaterial is impregnated with an aqueous solution of atetrakis(hydroxymethyl)phosphonium compound, preferably partiallyneutralized tetrakis(hydroxymethyl)phosphonium chloride, the impregnatedmaterial is at least partially dried, e.g., to about 5 to 25 percent byweight moisture retention, without fixation of the phosphonium compoundon the material, the partially dried material is cooled and then treatedwith dry ammonia gas optionally in the presence of water vapor wherebythe phosphonium compound is cured on the material and a fireretardantcharacter is imparted thereto.

8 Claims, No Drawings This invention relates to a processof producingflame retardant cellulosic containing materials. More particularly itrelates to a process of incorporating a phospho-- rus containing polymerin and on cellulosic containingmaterials.

BACKGROUND OF INVENTION The treatment of cellulosic containing materialsto impart fire-retardant characterthereto has been the subject of mucheffort and many such processes have been proposed. However most, if notall, of these known procedures have. defects which militate againsttheir complete acceptance by those working, in this area. I

As discussed in US. Pat. No. 3,236,676 many of the prior processesinvolving the use of tetrakis (hydroxymethyl)phosphonium condensationproduces to impart flame-resistant properties to cellulosic materialspossessed the defect of the tendency of the phosphonium compound tomigrate to the surface of the material during the curing step.

Another defect of the prior art processes resides in the undesirableeffects the flame retardant chemicals produce on the tensile propertiesof the treated materials.

U. S. Pat. No. 3,236,676 discloses a process wherein a phosphoniumcompound is fixed on the cellulosic material prior to curing with anagent such as ammonia. The process disclosed therein involves the stepsofimpregnating cellulosic materials with a solution of a tetrakis(hydroxymethyl) phosphonium salt, having a pH in the range of 3 to 9.5,heating the material between 100 C and 180 C., to dry the material andto fix the phosphonium salt on the fiber and thereafter treating theheat treated material with ammonia to cure the phosphonium salt on thematerial. This procedure, while generally successful in impartingflame-resistance to cellulosics has the disadvantages of requiring theheat fixation step, an additional processing step requiring theexpenditure of time and capital, and often results in the tendering orotherwise depreciating the physical character of the cellulosicmaterial.

OBJECTS OF THE INVENTION It is thus a principal object of this inventionto devise a process for imparting fire retardancy to cellulosiccontaining materials which does not otherwise alter the physicalproperties of the treated material.

Another object is to devise a simple, economical, and effective processfor treating cellulosic containingw materials with aqueous solutions oftetrakis(hydroxymethyl) phosphonium compounds to render such materialsfire-retardant.

Other objects will be obvious from the following description of thisinvention.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the presentinvention, cellulosic containing material is impregnated with a solutioncontaining tetrakis(hydroxymethyl )phosphonium chloride, or a partiallyneutralized derivative thereof, the impregnated material is heated to atleast partially dry it, without fixation of the phosphonium compoundthereon, and then, after cooling the heated material,

DETAILED DESCRIPTION OF THE INVENTION A preferred mode of carrying outthe process of the present invention comprises padding a cotton clothwith an aqueous solution of about 20 to about 40 percent by weight oftetrakis(hydroxymethyl)- phosphonium chloride which has been partiallyneutralized with about to about percent of the stoichiometric amount ofcaustic alkali. The padded cloth, containing about 25 to percent of itsweight of the padding liquor, is dried at least partially, preferably toabout 5 to about 25 percent moisture retention, without fixation of thephosphonium compound on the cloth, the partially dried cloth, is cooledand then is exposed to gaseous ammonia, preferably in the presence ofwater vapor to fix the phosphonium compound on the cloth, and thereby toimpart thereto fire-retardant properties which are fast to repeatedwashings. The treated cloth is preferably rinsed with an aqueoussolution of an oxidizing agent, such as hydrogen peroxide, sodiumperborate and the like, which after treatment removes color and odorfrom the treated material.

The padding solution used may be merely an aqueous solution oftetrakis(hydroxymethyl)phosphonium chloride. However such solutions havea pH value of about 1 and may be detrimental to the textile materialbeing treated. Preferably the solution is partially neturalized to a pHwithin the range of about 5 to 6.5. Alkaline materials such as sodium orpotassium hydroxides, soda ash, organic amines such as triethanolarnine,triethyl amine and the like can be used to adjust the pH of the paddingliquor.

It is preferred to dry the impregnated cloth, to remove at least aportion of the aqueous liquor. This drying step can be effected in adrying oven, by moving the padded cloth over heated cans, by hotpressing the cloth, and the like. Preferably the impregnated material isdried to a 5 to 25 percent by weight moisture retention. It has beenfound that this partial drying of the impregnated material does notresult in the fixation of any noticable amount of the phosphoniumcompound on the fiber. It has also been found that the impregnatedmaterial can be dried substantially completely, at a moderatetemperature, e.g., about 200 degrees Fahrenheit, without fixation of thephosphonium compound, and thereafter the dried material cooled byrewetting before treating with ammonia to fix the phosphonium compound.

Following the drying of the padded material, it has been found essentialto cool the material prior to passage thereof into the curing apparatus.It has been found that by curing the dried impregnated materialimmediately aftr removal from the drier, or by maintaining the driedmaterial hot, as by immediately placing and holding the material betweenlayers of insulating cloth and then curing the resin on the material,little or no fixation of the resin on the material occurs on curing.Accordingly, it is an essential step of the process of this invention,to cool the material after removal from the drier for at least about oneminute and preferably longer. Cooling of the hot dried material can beaccomplished by holding the material at ambient temperature in air, bypassing the material through a cold box, over cold cans or by sprayingwith water or the like.

Other salts than tetrakis(hydroxymethyl)phosphonium chloride can beused. Thus the corresponding acetate, bromide, sulfate, phosphate andthe like can be used. The chloride, being the salt commonly availablecommercially, is preferred for this reason. The following examples willillustrate the process of the present invention. Parts and percentagesare by weight and temperatures are given in degrees Fahrenheit, unlesotherwise indicated.

EXAMPLE l A 40 percent aqueous solution of tetrakis(hydroxymethyl)phosphonium chloride was partially neutralized with about 80 percent ofthe theoretical amount of sodium hydroxide. The resulting solution wasused to pad samples of 4.5 ounce per square yard cotton flannel. Thepadded cloth was then heated in a 200 oven for times specified in thefollowing table. The partially dried cloth was extracted with water. Asample of the extract was evaporated to dryness and the residueanalyzed.

About parts of the extract was admixed with 50 parts of methanol and themixture was gassed with ammonia until no further reaction was evident.The precipitate which formed was separated by filtration, dried andanalyzed. The results obtained are set out in the following table.

TABLE 1 Sample Sample Sample I 2 3 Wt. of F1annel-parts 39.6 37.3 38.5Wt of Sample after Padding-parts 82.2 78.7 79.6 Time of Drying at 200minutes 7.5 1.75 0 Wt. of aqueous Extractparts 4 l .9 39.5 40.9 Analysisof Extracted Solid Carbon 24.9 24.9 23.7 Hydrogen 6.7 6.9 6.9Phosphorous 16.6 16.0 16.0 Chlorine 11.3 13.3 11.1 Wt. of Extract SampleTaken 5.1 5.1 5.2 Wt. of Ppt. 2.7 2.9 2.7 m.p. of Ppt C. 211-212 211-212211-212 Analysis of Ppt Carbon 32.2 34.4 32.9 (38.4) Hydrogen 6.2 6.76.2 Nitrogen 13.7 14.7 13.9 (14.3) Phosphorous 23.9 25.7 23.7 (27.1

(Data in parentheses are analytical results from a product obtained bypassing ammonia into an aqueous solution of tetrakis(hydroxymethy1)-phosphonium chloride).

These data indicate that the drying and/or heating of the phosphoniumcompound on the cloth does not fix or chemically alter the compound inthis process.

EXAMPLE 2 This experiment illustrates the effect of cooling, i.e., thetemperature of the padded cloth at the time of the curing step on theamount of resin fixed on the cloth.

An aqueous solution containing 27.5 percent oftetrakis-(hydroxymethyl)phosphonium chloride was neutralized with aboutpercent of the stoichiometric amount of sodium hydroxide to give 27.5percent of the partially neutralized species. Samples of 4.5 ounce persquare yard of cotton flannel were impregnated with this solution to awet pick up of about -95 percent. The impregnated cloth samples weredried for various periods at 200 and then exposed to gaseous ammonia tocure the resin. The treated material was then scoured in an aqueousalkaline bath containing sodium perborate and dried. Two of the sampleswere treated thusly directly from the drier with a relatively short,i.e., about 2 to 3 minutes cooling period. One sample was taken from thedrier held in air for about one minute and passed over a perforated pipeemitting steam and then exposed to ammonia gas. One sample was passedover the perforated pipe emitting steam twice. Two samples were removedfrom the drier, held hot by placing in a hot pressing iron for about 5minutes and immediately inserted between insulated cloth layers tominimize cooling and then exposed to ammonia gas. The weight of curedresin fixed to the cloth samples was determined in each instance. Thetreated samples were evaluated for fire retardance according to AATCCStandard Test Method 34-1966, initially, after 10 standard home washesand after 25 such washes.

The data obtained in these tests are set out in the following Table 11.

TABLE II Sample 1 2 3 4 5 6 'IHPC, percent 27. 5 27. 5 2 7. 5 27. 5 27.5 27. 5 Wet pick up, percent- 91 96 94 95 96 Dried time at 200 2 6 1 6 16 3 6 3 6 Resin in cured sample, percent. 13.2 16.0 14.5 11.6 0 0Initial char, in. 4. 3 2. 5 3. 7 5. 0 Burn Burn 10 Home washes.. 5.1 5.05. 0 6. 2 Burn Burn 25 home washes 4. 0 4. 2 4. 6 5.0 Burn Burn 1Steamed by passing over perforated pipe once. I Steamed by passing overperforated pipe twice. {Heated in pressing iron and 119511191: W

These data indicate that heating the dried cloth without cooling beforecuring results in no resin add on. They also indicate the equivalence ofcuring the partially dried cloth after cooling with or without steammg.

EXAMPLE III In the manner described in Example 2, above, samples of 4.5ounce cotton flannel were impregnated with a 27.5 percent aqueoussolution of partially neutralized tetrakis(hydroxymethyl)phosphoniumchloride. The samples were then heated at 200 for periods indicated inthe following table following which the partially dried samples weretreated as follows.

One sample was removed from the drier, held in air for about one minuteand exposed to gaseous ammonia.

One sample was removed from the drier, held in air for about one minute,immediately heated in a flat bed press, removed therefrom, placedbetween layers of insulated cloth to prevent cooling and then exposed togaseous ammonia.

One sample was removed from the drier, held in air for at least oneminute, passed over a perforated pipe emitting steam and then exposed togaseous ammonia.

One sample removed from the drier, passed two times over the perforatedsteam pipe and then exposed to gaseous ammonia.

One sample removed from the drier, placed in the flat bed press, sprayedwith a fine water mist spray, and then exposed to gaseous ammonia.

Four samples removed from the drier, held for about 16 hours at ambienttemperature and then exposed to gaseous ammonia.

All samples were weighed to determine the amount of resin add on andevaluated for fire retardance.

The data from this series of tests are compiled in the following TableIII.

16.5, 17.4, and 17.5 percent respectively. The partially dried sampleswere cooled slightly and then exposed to a mixture of gaseous ammoniaand wet steam by passing the samples over a perforated pipe emitting thesteam-ammonia mixture. The cured samples were scoured in an aqueousalkaline bath containing sodium perborate.

Each of the cured resin impregnated cloth samples was tested for fireretardance and found to possess equivalent retardance which waspermanent, that is the samples were still about equally resistant tocharing even after 50 home washes.

By contrast, a sample of the cotton flannel was impregnated with theaqueous solution as described TABLE III Sample 1 2 3 4 5 6 7 s 9Partially neutralized THPC.percent 27.5 27.5 27.5 27.5 27.5 27.5 27.527.5 27.5. Wet pick up, percent 91 93 93 92 97 92 91 90 89. Dry time at200" ,Imin 6 6 a 6 a 6 10 2. Treatment N 0ne Hot time. One pass Two passHot cure Hold 16 Hold 16 Hold 16 Hold 16 steam. steam. spray. hrs. hrshrs. rs. Resin add on, percent 11.2 2.0 9.9 13.7 11.3 10. Initial char,in 20.0 Burns... 3.6 3.0 4.1 10 hornew 4. J 4.0 3.2 5.5L home wash 3.8do 3.7 4.2

These data indicate that resin impregnated on hot above and theimpregnated cloth was heated for one wet cloth will cure better thanresin impregnated on hot dry cloth; that resin impregnated on cool wetcloth will cure better than resin on hot wet cloth and that sprayingwith a water mist, steaming or holding for an extended period willreactive resin on a hot dry cloth substrate.

EXAMP E 4 An aqueous solution containing 22.5 percent of partiallyneutralized (85 percent) tetrakis(hydroxymethyl)phosphonium chloride,was used to impregnate three samples of 4.5 ounce cotton flannel. Thewet pick up of the three samples was 92.5, 91.7, and 94.5 percentrespectively.

One sample was held for about 16 hours at ambient temperature, and theresin add on was 15.7 percent, after exposure to gaseous ammonia. Thecloth sample was tested for fire retardance and found to give an initialchar of 3.7 inches.

The other two samples were heated at 200 for 1.5 and 3.0 minutesrespectively and the partially dried cloth hung in air at ambienttemperature for about 16 hours, and then cured.

The resin add on of these two samples was 14.6 and 17.3 percentrespectively.

Both of these samples were fire retardant giving an initial char of 4.2and 3.8 inches respectively.

These experiments show that impregnated material can be cured even aftera holding period following partial drying without effect on the fireretardant characteristic. g

, XAMP E5 An aqueous solution containing 22.5 percent of partiallyneutralized tetrak-is( hydroxymethyl )phosphonium chloride was used toimpregnate samples of 4.5 ounce cotton flannel. The samples had an addon of between about 85 and 90 percent.

The samples (three) were partially dried for one minute at 200, for 1.75minutes at 200 and for 1.75 minutes at 250. The resin add on wasdetermined to be minute at 200. The heated cloth was then exposed to amixture of an ammonia gas and air to cure the resin on the cloth. Theresin add on in this instance was 15.6 percent. The fire retardantcharacteristic of the treated cloth was substantially the same as thatof the above samples. However, after 50 home washes, the fire retardanceof this sample was substantially inferior to the above samples, the charincreasing to about twice of that of the initial char length (3.94 inchinitial; 6.58 inch after 50 home washes).

These data indicate the permanence of the fire retardant character ofthe material when cured with gaseous ammonia in the presence of watervapor.

What is claimed. is:

1. A method for producing fire retardant cellulosic containing materialswhich comprises a. impregnating a cellulosic containing material with anaqueous composition comprising a tetrakis(hydroxymethyl)phosphoniumcompound or a partially neutralized derivative thereof,

b. heating to at least partially dry the impregnated material withoutfixing the phosphonium compound thereon,

c. cooling said material for at least about one minute,

and

d. treating said material with gaseous ammonia or mixtures of gaseousammonia and water vapor to produce a substantially insoluble polymerformed from said phosphonium compound and ammonia on and in saidcellulosic containing material.

2. The method of claim 1 wherein the impregnated material contains from5 to 25 percent by weight moisture retention after the heating step.

3. The method of claim 1 wherein the impregnated material is held atambient temperature for at least about 1 minute after the heating step.

4. The method of claim 1 wherein the cooled material is exposed to steamand gaseous ammonia.

5. The method of claim 1 wherein the cooled material is exposed togaseous ammonia.

. compound 8. The method of claim 1 wherein the phosphonium compound istetrakis(hydroxymethyl)phosphonium chloride partially neutralized withfrom about '70 to about percent of the stoichiometric amount of acaustic alkali.

2. The method of claim 1 wherein the impregnated material contains from5 to 25 percent by weight moisture retention after the heating step. 3.The method of claim 1 wherein the impregnated material is held atambient temperature for at least about 1 minute after the heating step.4. The method of claim 1 wherein the cooled material is exposed to steamand gaseous ammonia.
 5. The method of claim 1 wherein the cooledmaterial is exposed to gaseous ammonia.
 6. The method of claim 1 whereinthe heated material is cooled by spraying with water and thereafterexposed to gaseous ammonia.
 7. The method of claim 1 wherein phosphoniumcompound is tetrakis(hydroxymethyl)phosphonium chloride.
 8. The methodof claim 1 wherein the phosphonium compound istetrakis(hydroxymethyl)phosphonium chloride partially neutralized withfrom about 70 to about 90 percent of the stoichiometric amount of acaustic alkali.